PUitiNGTON.] 
HYDRAULIC MINING, 
133 
as the square of the velocity and also depends on the condition of the 
pipes. Even the rivet heads in a pipe Line cause friction and conse 
quent loss of head. As Mr. George II. Evans a points out, it makes 
no difference whether the water is flowing up hill or down, or the 
pressure great or small, the total friction will be materially the same. 
-====zzl 
Fig. 26. — Pipe wrench for setting and unsetting hydraulic pipe. 
In wooden pipes the friction is nearly double that in iron or steel 
pipes. Cox's formula for finding the friction head, which must be 
subtracted from the actual head to give the effective head, is as 
follows: 
H =i25b x < 4 x V! + 5V - 2 > 
H =friction head in feet, 
'/^diameter of pipe in inches. 
L —length of pipe in feet. 
V=velocity of water in feet per second. 
Pig 27.— Method of bracing hydraulic pipe on steep slope 
The loss in head of a pipe line 12 inches in diameter, discharging 
400 miner's inches, and 5,000 feet in length, is computed by Mr. Evans 
to be 246.44 feet. Or, if the actual head is 500 feet, the effective head 
s reduced to 253.56 feet, or an original pressure of 217 pounds per 
square inch to 110 pounds. To find the velocity in feet per minute in 
((Practical Notes on Hydraulic Mining, San Francisco, 1898, p. 25. 
